The present invention relates to an active power factor controller and more particularly to a fully-integrated, fully-protected active power factor controller that operates in a critical-conduction mode and provides for high PF, low Total Harmonic Distortion (THD) and stable DC Bus regulation and includes an over-current protection together with the RDS(on) of the PFC MOSFET assembled with a MOSFET in single package.
In most electronic devices it is necessary to have the circuit act as a pure resistive load to the AC input line voltage. The degree to which the circuit matches a pure resistor is measured by the phase shift between the input voltage and input current and how well the shape of the input current waveform matches the shape of the sinusoidal input voltage. The cosine of the phase angle between the input voltage and input current is defined as the power factor (PF), and how well the shape of the input current waveform matches the shape of the input voltage is determined by the THD. A power factor of 1.0 (maximum) corresponds to zero phase shift and a THD of 0% represents a pure sine wave (no distortion). For this reason it is desirable to have a high PF and a low THD.